Method for Evaluating Proximity to Niagaran Reefs of Michigan Basin
Ronald J. Dehaas
A simple but effective technique for evaluating the relative structural
position of any exploratory Niagaran reef test is the "reefal structure
section
." This schematic
section
has the appearance of a
cross
section
; however,
geographic location does not determine the position of any individual test on
the
section
. Instead, all holes in a local (approximately 2-mi2 area)
are sorted strictly by subsea elevation of the Niagaran Brown unit. The reefal
structure
section
is then generated with the highest Niagaran Brown unit on the
right, progressing to the lowest Niagaran Brown unit on the left, all hung on a
subsea datum.
Reefal structure sections clearly show the relative position of each test to
the reef. Invariably, dry off-reef holes line up on the left side of the
section
, and productive (or dry on-reef) wells line up on the right side of the
section
. These sections are useful as an exploration tool in determining which
holes in an area are near undiscovered reefs. They are also useful in the field,
while drilling, as a predictive tool in projecting expected depths of
formations.
When applied to a regional structural-stratigraphic framework, reefal structure sections are also useful in indicating which formations thin over reefs in different areas.
AAPG Search and Discovery Article #91041©1987 AAPG
Eastern Section
Meeting, Columbus, Ohio, October 7-10, 1987.